For the purposes of anatomic orientation, when the body is viewed in the upright position it has 3 orthogonal axes: superior-inferior (up-down), posterior-anterior (back-front), and right-left.
In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers as seen in FIG. 1: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary, and are each mounted in an annulus comprising dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. Each annulus defines a flow orifice. The tricuspid and mitral valves together define the atrioventricular (AV) junctions.
The atriums are the blood-receiving chambers, which pump blood into the ventricles. The ventricles are the blood-discharging chambers. A wall composed of fibrous and muscular parts, called the interatrial septum separates the right and left atriums (see FIGS. 2 to 4). The fibrous interatrial septum is a materially stronger tissue structure compared to the more friable muscle tissue of the heart. An anatomic landmark on the interatrial septum is an oval, thumbprint sized depression called the oval fossa, or fossa ovalis (shown in FIG. 4).
The synchronous pumping actions of the left and right sides of the heart constitute the cardiac cycle. The cycle begins with a period of ventricular relaxation, called ventricular diastole. The cycle ends with a period of ventricular contraction, called ventricular systole. The four valves (see FIGS. 2 and 3) ensure that blood does not flow in the wrong direction during the cardiac cycle; that is, to ensure that the blood does not back flow from the ventricles into the corresponding atria, or back flow from the arteries into the corresponding ventricles. The mitral valve is between the left atrium and the left ventricle, the tricuspid valve between the right atrium and the right ventricle, the pulmonary valve is at the opening of the pulmonary artery, and the aortic valve is at the opening of the aorta.
FIGS. 2 and 3 show the anterior (A) portion of the mitral valve annulus abutting the non-coronary leaflet of the aortic valve. The mitral valve annulus is in the vicinity of the circumflex branch of the left coronary artery, and the posterior (P) side is near the coronary sinus and its tributaries.
The mitral and tricuspid valves are defined by fibrous rings of collagen, each called an annulus, which forms a part of the fibrous skeleton of the heart. The annulus provides peripheral attachments for the two cusps or leaflets of the mitral valve (called the anterior and posterior cusps) and the three cusps or leaflets of the tricuspid valve. The free edges of the leaflets connect to chordae tendineae from more than one papillary muscle, as seen in FIG. 1. In a healthy heart, these muscles and their tendinous chords support the mitral and tricuspid valves, allowing the leaflets to resist the high pressure developed during contractions (pumping) of the left and right ventricles.
When the left ventricle contracts after filling with blood from the left atrium, the walls of the ventricle move inward and release some of the tension from the papillary muscle and chords. The blood pushed up against the undersurface of the mitral leaflets causes them to rise toward the annulus plane of the mitral valve. As they progress toward the annulus, the leading edges of the anterior and posterior leaflet come together forming a seal and closing the valve. In the healthy heart, leaflet coaptation occurs near the plane of the mitral annulus. The blood continues to be pressurized in the left ventricle until it is ejected into the aorta. Contraction of the papillary muscles is simultaneous with the contraction of the ventricle and serves to keep healthy valve leaflets tightly shut at peak contraction pressures exerted by the ventricle.
In a like manner, the tricuspid valve controls the backflow of blood from the right ventricle into the right atrium during contraction of the right ventricle. Contraction of the right ventricle occurs simultaneously with contraction of the papillary muscles, keeping the healthy tricuspid valve leaflets shut at peak ventricular contraction pressures. Tricuspid regurgitation involves backward flow of blood across the tricuspid valve into the right atrium. The most common cause of tricuspid regurgitation is not damage to the valve itself but enlargement of the right ventricle, which may be a complication of any disorder that causes failure of the right ventricle. Other diseases can directly affect the tricuspid valve. The most common of these is rheumatic fever, which is a complication of untreated strep throat infections. The valve fails to close properly, and blood can flow back to the right atrium from the right ventricle, and from there back into the veins. This reduces the flow of blood forward into the lungs.
Various surgical techniques may be used to repair a diseased or damaged valve. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve. Another less drastic method for treating defective valves is through repair or reconstruction, which is typically used on minimally calcified valves. By interrupting the cycle of progressive functional mitral regurgitation, studies have shown increased survival and even increased forward ejection fraction in many surgical patients. The problem with surgical therapy is the significant insult it imposes on these chronically ill patients with high morbidity and mortality rates associated with surgical repair.
Surgical edge-to-edge juncture repairs, which can be performed endovascularly, are also made, in which a mid-valve leaflet to mid-valve leaflet suture or clip is applied to keep these points of the leaflet held together throughout the cardiac cycle. Other efforts have developed an endovascular suture and a clip to grasp and bond the two mitral leaflets in the beating heart. Grade 3+ or 4+ organic mitral regurgitation may be repaired with such edge-to-edge technologies. This is because, in organic mitral regurgitation, the problem is not the annulus but in the central valve components. However, functional mitral regurgitation can persist at a high level, even after edge-to-edge repair, particularly in cases of high Grade 3+ and 4+ functional mitral regurgitation. After surgery, the repaired valve may progress to high rates of functional mitral regurgitation over time.
In yet another emerging technology, the coronary sinus is mechanically deformed through endovascular means applied and contained to function solely within the coronary sinus.
One repair technique that has been shown to be effective ill treating incompetence is annuloplasty, or reconstruction of the ring (or annulus) of an incompetent cardiac valve. The repair may be done entirely surgically, by cutting out a segment of leaflet and re-attaching the cut sides with sutures. However, more typically the annulus is reshaped by attaching a prosthetic annuloplasty repair segment or ring thereto. For instance, the goal of a posterior mitral annulus repair is to bring the posterior mitral leaflet forward toward to the anterior leaflet to better allow coaptation. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation and valve integrity to prevent reverse flow while permitting good hemodynamics during forward flow.
The annuloplasty ring typically comprises an inner substrate or core of a metal such as a rod or multiple bands of stainless steel or titanium, or a flexible material such as silicone rubber or Dacron cordage, covered with a biocompatible fabric or cloth to allow the ring to be sutured to the fibrous annulus tissue. More rigid cores are typically surrounded by an outer cover of both silicone and fabric as a suture-permeable anchoring margin. Annuloplasty rings may be stiff or flexible, split or continuous, and may have a variety of shapes in plan view, including circular, D-shaped, C-shaped, or kidney-shaped. Examples are seen in U.S. Pat. Nos. 5,041,130, 5,104,407, 5,201,880, 5,258,021, 5,607,471 and, 6,187,040. In the context of the present invention, the term annuloplasty ring encompasses rings both open (e.g., C-shaped) and closed (e.g., D-shaped), as well as shorter segments, bands, or other such terms for a prosthesis that at least partly encircles and attaches to an annulus to reshape or correct a dysfunction in the annulus.
Most rigid and semi-rigid annular rings for the mitral valve have a kidney-like or D shape, with a relatively straight anterior segment co-extensive with the anterior valve leaflet, and a curved posterior segment co-extensive with the posterior valve leaflet. The shape of the annular rings reproduces the configuration of the valve annulus during the ventricular systole, and therefore in the stage of the valve closing. The ratio between minor axis and major axis is typically 3:4 in most models currently on the market since it reproduces normal anatomical ratios. Most of the earlier mitral rings were planar, while some (e.g., U.S. Pat. Nos. 5,104,407, 5,201,880, and 5,607,471) are bowed upward on their anterior segment (and slightly on their posterior segment) to accommodate the three-dimensional saddle shape of the anterior aspect of the mitral annulus. Newer rings have larger posterior bows (e.g., U.S. Pat. Nos. 6,805,710 and 6,858,039), or other three-dimensional configurations.
Tricuspid rings are sold in various configurations. For example, the Carpentier-Edwards Classic® Tricuspid Annuloplasty Ring sold by Edwards Lifesciences Corporation of Irvine, Calif., is a C-shaped ring with an inner titanium core covered by a layer of silicone and fabric. Rings for sizes 26 mm through 36 mm in 2 mm increments have outside diameters (OD) between 31.2-41.2 mm, and inside diameters (ID) between 24.3-34.3 mm. These diameters are taken along the “diametric” line spanning the greatest length across the ring because that is the conventional sizing parameter.
Correction of the aortic annulus requires a much different ring than for a mitral annulus. For example, U.S. Pat. Nos. 5,258,021 and 6,231,602 disclose sinusoidal or so-called “scalloped” annuloplasty rings that follow the up-and-down shape of the three cusp aortic annulus. Such rings would not be suitable for correcting a mitral valve deficiency.
In the usual annuloplasty ring implant procedure, an array of separate implant sutures are first looped through all or portions of the exposed annulus at intervals spaced equidistant from one another, such as for example 4 mm intervals. The surgeon then threads the implant sutures through the annuloplasty ring at more closely spaced intervals, such as for example 2 mm. This occurs with the prosthesis outside the body, typically secured to a peripheral edge of a holder or template. Despite the advantage of increases visibility, instances of snagging of the inner core with the implant sutures have occurred.
The ring on the holder is then advanced (parachuted) distally along the array of pre-anchored implant sutures into contact with the valve annulus, thus effecting a reduction in valve annulus circumference. At this point a handle used to manipulate the holder or template is typically detached for greater visibility of the surgical field. The surgeon ties off the implant sutures on the proximal side of the ring, and releases the ring from the holder or template, typically by severing connecting sutures at a series of cutting guides. Although sutures are typically used, other flexible filaments to connect the ring to the holder may be suitable. Because of the presence of multiple implant and connecting sutures in the surgical fields, the step of disconnecting the ring from the holder with a scalpel is somewhat delicate, and can be confusing for the novice. It should be noted that a similar holder connection and implant procedure, with attendant drawbacks, are also common for implanting prosthetic valves.
The present application has particular relevance to the repair of the tricuspid valve, which regulates blood flow between the right atrium and right ventricle, although certain aspects may apply to repair of other of the heart valves.
Four structures embedded in the wall of the heart conduct impulses through the cardiac muscle to cause first the atria then the ventricles to contract. These structures are the sinoatrial node (SA node), the atrioventricular node (AV n-ode), the bundle of His, and the Purkinje fibers. On the rear wall of the right atrium is a barely visible knot of tissue known as the sinoatrial, or SA node. This tiny area is the control of the heart's pacemaker mechanism. Impulse conduction normally starts in the SA node. It generates a brief electrical impulse of low intensity approximately 72 times every minute in a resting adult. From this point the impulse spreads out over the sheets of tissue that make up the two atria, exciting the muscle fibers as it does so. This causes contraction of the two atria and thereby thrusts the blood into the empty ventricles. The impulse quickly reaches another small specialized knot of tissue known as the atrioventricular, or AV node, located between the atria and the ventricles. This node delays the impulse for about 0.07 seconds, which is exactly enough time to allow the atria to complete their contractions. When the impulses reach the AV node, they are relayed by way of the several bundles of His and Purkinje fibers to the ventricles, causing them to contract. As those of skill in the art are aware, the integrity and proper functioning of the conductive system of the heart is critical for good health.
FIG. 5 is a schematic view of the tricuspid valve orifice seen from its inflow side (from the right atrium), with the peripheral landmarks labeled as: antero septal commissure, anterior leaflet, posterior commissure, antero posterior leaflet, postero septal commissure, and septal leaflet. Contrary to traditional orientation nomenclature, the tricuspid valve is nearly vertical, as reflected by these sector markings.
From the same viewpoint, the tricuspid valve 20 is shown surgically exposed in FIG. 6 with an annulus 22 and three leaflets 24a, 24b, 24c extending inward into the flow orifice. Chordae tendineae 26 connect the leaflets to papillary muscles located in the RV to control the movement of the leaflets. The tricuspid annulus 22 is an ovoid-shaped fibrous ring at the base of the valve that is less prominent than the mitral annulus, but larger in circumference.
Reflecting their true anatomic location, the three leaflets in FIG. 6 are identified as septal 24a, anterior 24b, and posterior (or mural) 24c. The leaflets join together over three prominent zones of apposition, and the peripheral intersections of these zones are usually described as commissures 28, separately identified above. The leaflets 24 are tethered at the commissures 28 by the fan-shaped chordae tendineae 26 arising from prominent papillary muscles originating in the right ventricle. That portion of the annulus 22 at the base of the septal leaflet 24a is the site of attachment to the fibrous trigone, the fibrous “skeletal” structure within the heart. The anterior leaflet 24b, largest of the 3 leaflets, often has notches. The posterior leaflet 24c, smallest of the 3 leaflets, usually is scalloped.
The ostium 30 of the right coronary sinus opens into the right atrium, and the tendon of Todaro 32 extends adjacent thereto. The AV node 34 and the beginning of the bundle of His 36 are located in the supero-septal region of the tricuspid valve circumference. The AV node 34 is situated directly on the right atrial side of the central fibrous body in the muscular portion of the AV septum, just superior and anterior to the ostium 30 of the coronary sinus 30. Measuring approximately 1.0 mm×3.0 mm×6.0 mm, the node is flat and oval. The AV node 34 is located at the apex of the triangle of Koch 38, which is formed by the tricuspid annulus 22, the ostium 30 of the coronary sinus, and the tendon of Todaro 32. The AV node 34 continues on to the bundle of His 36, typically via a course inferior to the commissure 28 between the septal 24a and anterior 24b leaflets of the tricuspid valve; however, the precise course of the bundle of His 36 in the vicinity of the tricuspid valve may vary. Moreover, the location of the bundle of His 36 may not be readily apparent from a resected view of the right atrium because it lies beneath the annulus tissue.
The triangle of Koch 38 and tendon of Todaro 32 provide anatomic landmarks during tricuspid valve repair procedures. A major factor to consider during surgery is the proximity of the conduction system (AV node 34 and bundle of His 36) to the septal leaflet 24a. Of course, surgeons must avoid placing sutures too close to or within the AV node 34. C-shaped rings are good choices for tricuspid valve repairs because they allow surgeons to position the break in the ring adjacent the AV node 34, thus avoiding the need for suturing at that location.
An example of a rigid C-shaped ring is the Carpentier-Edwards Classic® Tricuspid Annuloplasty Ring discussed above. The Classic® ring has a gap between free ends. The gap provides a discontinuity to avoid attachment over the AV node. The gap for the various sizes ranges between about 5-8 mm, or between about 19%-22% of the labeled size.
Despite numerous designs presently available or proposed in the past, there is a need for a prosthetic tricuspid ring that better repairs certain conditions of the tricuspid annulus, and in particular reduces excessive chordal tethering, which tends to pull the leaflets apart leading to regurgitation.